Electrical Potential Difference Research Articles

Relative relevance of factors affecting the electrokinetic dewatering of soft clayey soils

Electrokinetic (EK) treatment is becoming increasingly important in the geotechnical field, especially for treating fine-grained soils. Above all, dredged sediments (slurries) need to be treated in order to be reutilised. Applying an electric potential difference within the soil, three phenomena take place: electrophoresis, electro-osmosis and electromigration. Negative particles move towards the positive electrode while water and cations move towards the negative electrode. Although the literature is full of cases describing the parameters that affect the EK process, there is a need to understand its limits and fields of application. This paper summarises the results collected from several case studies to understand the influence of some parameters on the efficiency of EK treatment, specifically in terms of dewatering rate. Soil conditions (soil type, pH, pore fluid salinity and water content) and set-up design parameters (electrode materials, configurations and operational mode) are analysed. Finally, parameter ranges for assessing the acceptability of electro-osmotic treatment are proposed. The results show that there are optimum values for the previously mentioned parameters that improve the dewatering and thus enhance the behaviour of the treated soils. EK treatment can be effective when applied on dredged sediments with low salinity.

Performance of ion intercalation materials in capacitive deionization/electrochemical deionization: A review

Abstract Capacitive deionization (CDI) also referred to as electrochemical deionization (EDI) is a deionization technology which depends on the electrical potential difference applied between a pair of electrodes to extract charged species from the solution. Due to their low cost, good electrical conductivity, porous structure, and high specific surface area, carbon materials have been the materials of choice for electrodes in most CDI cells. With carbon-based materials, ions from solution are extracted through electrosorption mechanism and stored in the electrical double layer (EDL) formed on the electrode surface. Recently, ion intercalation materials that store ions through pseudocapacitive ion intercalation have attracted interest. In pseudocapacitive ion intercalation mechanism, ions are inserted or stored in the lattice crystal structure sites of the intercalation host compounds (IHCs) due to redox reactions. The desalination performance of these materials, also referred to as salt adsorption capacity (SAC) and expressed in mg/g is reported to be higher compared to that of carbon-based electrode materials. The enhanced SAC of intercalation materials is due to the fact that ions are not only removed from the solution via surface adsorption but also through transfer of charge and intercalation/insertion of the ions into their crystallographic sites. To date, there is inadequate number of articles summarizing the performance of intercalation materials and strategies undertaken to improve performance thereof for desalination and ion separation purposes. This paper therefore, reviewed the performance of different intercalation electrode materials for water desalination presented in the literature to date. The discussion covers different geometries/architecture of a desalination cell utilizing ion intercalation materials, performance of ion intercalation materials and their mechanism of deionization as well as strategies that have been employed to improve their deionization performance. Furthermore, this paper provides an outlook and research niches existing in the field of ion intercalation materials for desalination applications and selective removal of both mono and divalent ions from aqueous solutions.

Thermally Induced Delamination of PV-TEG: Implication of Leg’s Joule and Thomson Heating

The thermal implication of peel stresses and Joule and Thomson heating on the delamination of photovoltaic-thermoelectric generator (PV-TEG) layers is modelled and established numerically. The scope of the study embraces simulation of the hybrid system with and without electric potential difference. Furthermore, the results obtained from the interfacial peel stresses demonstrate that uneven contractions occur in the layers of the hybrid system, resulting in delamination. In addition, the conductor strip/TEG interface has the highest peel stress with a numerical value of 0.13 GPa, while the glass/ethyl vinyl acetate (EVA) interface presents a contrasting stress pattern in comparison to the EVA/cell, EVA/back plate and conductor strip/TEG interface. However, the n-type leg of the TEG has a higher thermal stress in comparison to the entire system components resulting from the application of 7 mV electric potential. Finally, this paper demonstrates that thermal stress is extremely deleterious in the TEG in comparison to the PV module. As a result, device failures will commence from the thermoelectric legs, with the n-type leg having a shorter operational life in comparison to the p-type leg.

Evaluation of electrical signals in pine trees in a mediterranean forest ecosystem

ABSTRACT Electric potential differences in living plants are explained by theories based on sap flow. In order to acquire more advanced knowledge about the spatial distribution of these electric potential measures in trees, this research aims to analyze electrical signals in a population of Aleppo pines (Pinus halepensis Mill.) in a representative Mediterranean forest ecosystem. The specific research objective is to assess some of the most significant factors that influence the distribution pattern of those electric signals: tree age, measurement type and electrode placement. The research has been conducted in representative forest stands, obtaining measurements of different representative trees. After a statistical evaluation of the obtained results, the main conclusions of our research are: A.Tree maturity influences directly on electric potential. B.Maximum electrical signals can be measured in young pines showing values of 0.6 V and 0.6 µA for voltage and current, respectively. C.The distribution patterns of both voltage and short-circuit current depending on electrode placement are uniform.

Cisplatin influences the skin ion transport – An in vitro study

Platinum-based drugs, used in treating tumors, cause numerous undesirable effects in patients, like neuropathic pain, hypersensitivity, reddening, pruritus and rash. Changes in Na+ transport modify local osmolality and contribute to the initiation of hypersensitivity and allergy. They are also associated with stimulation of C-fibres and hyperalgesia. Cl− transport is essential for regulation of sweat composition and the migration of immunocompetent cells.The aim of the conducted study was to assess the effect of a cisplatin solution on the electrophysiological parameters of the isolated rabbit skin specimens. The difference in transepithelial electrical potential (PD) and resistance (R) in stationary conditions and during 15 s mechanical-chemical stimulation (PDmin and PDmax), were measured.Measurement of R revealed that tissue samples were live, and their permeability to ions were stable. Control specimens had PD -0.22 mV (median). The PD of specimens treated by cisplatin was -0.55 mV (median), to for cisplatin and bumetanide 0 mV (median). Treatment with cisplatin did not change the continuous transport of Na+ and K+ ions, but did change that of Cl− ions. Stimulation of samples with the transport blockers of Cl−, Na+ and both induced repeatable and measurable reactions in the transport of the appropriate ions. It was shown that absorption of Na+ ions and release of Cl− ions was intensified than in the untreated specimens.It was proven in the study that cisplatin influences the Na+ and Cl− transport in the skin cells. Restoring the balance in ion flow can prevent side effects of use cisplatin-based drugs.

On the dynamics of a novel energy harvester to convert the energy of the magnetic noise into electrical power

Abstract Magnetic and mechanical noise in the frequency range of MHz are available in the environment and could be harvested for human convenience. This manuscript focuses on the dynamical behavior of hybrid magneto-mechano-electric (MME) energy harvesters to convert the energy of the magnetic noise and mechanical noise to electrical power using a composite energy scavenging structure. The proposed apparatus is composed of a piezoelectric (PZT-5A) layered beam on which a magnetostrictive material (Metglas-2605SC) is deposited. Once the device is exposed to external magnetic noise, Metglas-2605SC undergoes mechanical strain, and as a result, the mechanical strain is converted to electrical potential difference throughout the PZT-5A layer. In the present manuscript, the energy harvesting device is modeled as a cantilever beam, and the equations of motion are derived using Newton’s second law. The governing equations of motion, along with the output electrical potential difference equation are then discretized and numerically integrated over time, the frequency response curves for deflection, harvested power, and voltage are determined, and the effect of governing parameters on the output power is investigated. It is concluded that in the absence of mechanical damping, the response resembles that of a damped mass-spring oscillator confirming the energy consumption throughout the output circuit. In addition, as the external load resistance increases up to a particular value (164k Ω ), the attenuation rate of the response amplitude, and accordingly, the harvested power also increases. Beyond that particular value, the collected energy decreases by further increasing the load resistance. The results revealed that between two successive natural frequencies, there exists an anti-resonance region, where the response amplitude dramatically drops, and the operating area of the energy harvester needs to be kept well away from this zone in the frequency domain. The analytical results are verified by presenting a finite element simulation of the cantilever energy harvesting model, in which the distribution of stress and harvested voltage are determined.

Nanoscale Characteristics of Ocular Lipid Thin Films Using Kelvin Probe Force Microscopy.

PurposeTo describe the use of Kelvin probe force microscopy (KPFM) to investigate the electrical surface potential of human meibum and to demonstrate successful use of this instrument on both human meibum and a meibum model system (six-lipid stock [6LS]) to elucidate nanoscale surface chemistry and self-assembly characteristics.Materials and Methods6LS and meibum were analyzed in this study. Mica-supported thin films were created using the Langmuir-Blodgett trough. Topography and electrical surface potential were quantified using simultaneous atomic force microscopy/KPFM imaging.ResultsBoth lipid mixtures formed thin film patches on the surface of the mica substrate, with large aggregates resting atop. The 6LS had aggregate heights ranging from 41 to 153 nm. The range in surface potential was 33.0 to 125.9 mV. The meibum thin films at P = 5 mN/m had aggregates of 170 to 459 nm in height and surface potential ranging from 15.9 to 76.1 mV, while thin films at P = 10 mN/m showed an aggregate size range of 147 to 407 nm and a surface potential range of 11.5 to 255.1 mV.ConclusionsThis study showed imaging of the differences in electrical surface potential of meibum via KPFM and showed similarities in nanoscale topography. 6LS was also successfully analyzed, showing the capabilities of this method for use in both in vitro and ex vivo ocular research.Translational RelevanceThis study describes the use of KPFM for the study of ocular surface lipids for the first time and outlines possibilities for future studies to be carried out using this concept.

Epithelial tissue geometry directs emergence of bioelectric field and pattern of proliferation.

Patterns of proliferation are templated by both gradients of mechanical stress as well as by gradients in membrane voltage (Vm), which is defined as the electric potential difference between the cytoplasm and the extracellular medium. Either gradient could regulate the emergence of the other, or they could arise independently and synergistically affect proliferation within a tissue. Here, we examined the relationship between endogenous patterns of mechanical stress and the generation of bioelectric gradients in mammary epithelial tissues. We observed that the mechanical stress gradients in the tissues presaged gradients in both proliferation and depolarization, consistent with previous reports correlating depolarization with proliferation. Furthermore, disrupting the Vm gradient blocked the emergence of patterned proliferation. We found that the bioelectric gradient formed downstream of mechanical stresses within the tissues and depended on connexin-43 (Cx43) hemichannels, which opened preferentially in cells located in regions of high mechanical stress. Activation of Cx43 hemichannels was necessary for nuclear localization of Yap/Taz and induction of proliferation. Together, these results suggest that mechanotransduction triggers the formation of bioelectric gradients across a tissue, which are further translated into transcriptional changes that template patterns of growth.

Functional coupling between BKCa and SOC channels

High-conductance, voltage- and calcium-activated potassium channels (BKCa) and store-operated calcium channels (SOCs) are belong to K+ channels superfamily and calcium channels superfamily respectively. Since BKCa potassium channels can be activated by calcium ions, we set out to examine whether SOCs are coupled with BKCa and to probe the relationship of BKCa and SOCs. First, we proved that BKCa immunoprecipitated with Orai1, and confocal microscopy showed that BKCa co-localized with Orai1. Next, we mapped that the exact binding sites locate in the 350aa-371aa fragment of the first regulatory domain associated with K+ conduction (RCK1) and the 720aa-814aa fragment in the second regulatory domain associated with K+ conduction (RCK2) via GST-pull-down assays. Then, we showed, by calcium imaging that BKCa overexpression enhanced endogenous and exogenous store-operated calcium entry (SOCE) and this enhancement could be blocked by Orai1 knockdown. Finally, we proved that SOCE could enhance the activity of BKCa by patch-clamp. From these results we conclude that BKCa can form a positive feedback loop with SOCs, as the Ca2+ influx from SOCs can active BKCa, which can hyperpolarize the plasma membrane. In turn, the hyperpolarized membrane will form a higher electric potential difference and give more force, allowing Ca2+ influx via SOCs.

Mathematical modelling of electrical potential difference in a non-uniform electric field

This work offers an unproblematic teaching tool for the instruction of challeng-ing concept of electric potential difference in a non-uniform electric field. Specifically, mathematical modelling process is employed and managed to comprehend and teach exceedingly difficult concepts of uniform and non-uniform electric fields, electrical potential difference, scalar products of vectors and also concept of path integral. In order to accomplish those tasks, initially a basic conducting panel/sheet, that is simply a wet cardboard, is designed as a part of the apparatus, together with a dc power supply, a multi meter and connecting cables. The established method is interesting in the sense that the 3D wet cardboard is novel, very practical and minimal costing, hence the approach offers physics educators fresh teaching routes and opportunities to clarify the puzzling concept of electrical potential difference and further.

System electro-neutralizer of agrochemicals contained in food and water samples through electrons trap

Abstract This study presents a system to electro-neutralize agrochemicals in food and water samples based on the properties of a controlled electron trap, the related apparatus is protected under patent application (WO/2018/090110; INPI: BR 10 2016 0268486) / (PCT / BR 2017/050115). The efficacy of the system was verified as to the type, quantity, surface tension charge, temperature, pH and static energy loading of the electrolyte for both solid and liquid samples. It also took into consideration the retention and accumulation measurement of electric charges, verification of electrical potential differences and also accumulation by applying pulsed high voltage in according to the Daniell Cell method. The proposed technology is able to provide the electron-neutralization of acidic and alkaline chemicals and their toxic byproducts by modifying the pH of the liquid or solid medium. This is justified by the action of the electron trap using different polarities and electrodes in the range of 8 to 100 kV.

Laser processing of Mg-10Li-3Al-3Zn alloy：Part II- Improving corrosion resistance of multi-phase Mg alloys by laser surface processing

In Part Ⅰ of this series, it can be found that the corrosion resistance of metals in the welded seam zone (WSZ) was far higher than that of the base metal (BM) of MBLS10A-200 Mg-Li alloy. Therefore, the feasibility of improving the corrosion resistance of MBLS10A-200 Mg-Li alloy through laser surface melting (LSM) was further explored. Meanwhile, laser shock peening (LSP) treatment was also used for contrast. The results showed that the surface melted zone with the corrosion resistance through LSM superior to that of metals in WSZ of MBLS10A-200 alloy through laser welding can be prepared by controlling heat input through increasing the scanning speed of laser beam, while LSP has limited impact on the electrochemical corrosion resistance of MBLS10A-200 alloy. The corrosion current density (Jcorr) of the samples subjected LSM declined by two orders of magnitude compared with the base metal (BM) while the charge transfer resistance increased by 17 times compared with BM. An analysis indicated that owing to the fast cooling rate during laser processing, the multi-phase microstructures (i.e. α phase, β phase and Li2MgAl) of BM were transformed into β single-phase microstructure in WSZ and surface melted zone. In this way, not only solid solution strengthening of the metals in WSZ was realized but also the micro-galvanic coupling generated due to the difference of electric potentials of multi-phase microstructures were reduced, thus improving the corrosion resistance of surface melted zone.

Electro-elastic flow instabilities of viscoelastic fluids in contraction/expansion micro-geometries

Electro-elastic instabilities in electro-osmotic contraction/expansion flows (EOF) of viscoelastic fluids are experimentally investigated in this work. Several microchannel configurations are used, including the cases with hyperbolic-shaped contractions followed by an abrupt expansion, or abrupt contractions followed by a hyperbolic-shaped expansion. Such cases were selected to assist in the understanding of the EOF instability mechanisms and at which conditions they occur. A reference Newtonian fluid was also used in the experiments, and a wide range of electric fields were imposed to drive the flow. Flow visualizations for a Newtonian fluid allowed to assess the impact of dielectrophoresis on the velocity field of the seeding particles. For each geometry, depending on the polymer concentration, the flow was found to be quasi-Newtonian below a critical electric potential difference, characterized by smooth parallel steady flow patterns in the upstream and downstream channels. Above the critical voltage difference two types of electro-elastic instabilities were found to occur, leading to an unsteady symmetric flow, and to time-dependent irregular flow.

Electrocardiography Interpretation Competency of Medical Interns: Experience from Two Ethiopian Medical Schools.

Background Electrocardiography (ECG) is the graphical display of electrical potential differences of an electric field originating in the heart. Interpretation of ECG is a core clinical skill in the department of emergency medicine. The main aim of this survey was to assess competency of ECG interpretation among 2018 graduating class medical students in Addis Ababa University and Haramaya University. Methodology. A cross-sectional survey was conducted on medical interns at Addis Ababa University and Haramaya University. Data had been collected from October 01, 2018, to October 30, 2018, by using structured questionnaires. Data were entered, cleaned, edited, and analyzed by using SPSS version 25.0 statistical software. Descriptive statistics, cross-tabs, chi-squared test, Mann–Whitney U test, and binary logistic regression were utilized. Results Two-hundred and two graduating medical students were involved on this survey, out of which 61.3% (95% CI 56.3–66.3%) and 32.75% (95% CI 28.25–37.25) were able to correctly interpret the primary ECG parameters and the arrest rhythm of ECG abnormalities, respectively. The ability to detect from common emergency ECG abnormalities of anterioseptal ST segment elevation myocardial infraction, atrial fibrillation, and first-degree atrioventricular block was 42.6%, 39.1%, and 32.1%, respectively. Conclusion This survey showed graduating medical students had low competency in ECG interpretations.

Electrochemically Enhancing Nanostructured Fe-Oxide/Co3O4 for the Reverse Water Gas Shift Reaction

The abundant amount of CO2 in the atmosphere is a valuable resource that when managed correctly can replace energy from the fossil fuel industry and provide a carbon-neutral solution that will reduce the impacts of the climate and ecological crisis[1]. This is achieved by reducing CO2 with hydrogen (H2) through the reverse water gas shift (RWGS) reaction to produced carbon monoxide (CO). CO then acts as a source molecule in the Fischer-Tropsch synthesis to manufacture hydrocarbon fuels. Due to the high stability of the CO2 molecule, significant thermal energy is required to undertake the reaction. Iron-oxide (FeOx) has been shown to be an active and thermally stable catalysts towards the RWGS reaction. FeOx (iron-oxide) nanowires are fabricated through the polyol reduction method and have been characterized through scanning transmission electron microscopy (STEM) analysis[2]. Following the wet deposition method, the Fe nanowires are finely dispersed on cobalt-oxide (Co3O4) to act as a support and semi-conductor. The dispersion of Fe on Co3O4 enhances the electronic properties of the catalyst through the metal-support interaction (MSI) effect[3]. The MSI entails the back spillover of promoting oxygen (Oδ-) ionic species from Co3O4 to FeOx by an increase in temperature, altering the work function of FeOx and allowing to cycle oxygen from the breaking of CO2. Through the Electrochemical Promotion of Catalysis (EPOC) phenomenon the catalytic activity can be enhanced by altering the binding energy of the reactant and intermediate species on the catalytic surface[4]. The MSI and EPOC phenomena have been shown to be functionally equivalent in terms of the change in work function. The difference between them is that in EPOC the movement of ions can be controlled through the application of an electrical current or potential difference, while the MSI effect is controlled by a thermal input. EPOC entails the use of solid electrolytes, for instance yttria-stabilized zirconia (YSZ) and barium zirconate yttrium-doped (BZY) which are oxygen and proton conductors, respectively. The catalyst-working electrodes (i.e. FeOx nanowires) are deposited on one side of the electrolyte and on the opposite side, inert gold counter and reference electrodes. Through the application of a potential difference between the electrodes, promoting species migrate through the three-phase (solid-gas-catalyst) boundary in order to interact with the exposed-catalyst surface. In the case of BZY, when a potential difference is applied between the counter and working electrode, H+ are removed from the surface through the three-phase boundary (tpb) towards BZY, referred to as positive polarization. When the polarization is reversed from the working to counter electrode, H+ migrate from BZY through the tpb towards the catalytic surface. Utilizing YSZ, results in the opposite migration with O2- ions. Regardless of the type of solid electrolyte used the catalyst is oxidized under positive polarization and reduced under negative polarization. The use of the Co3O4 semiconductor allows to combine both the MSI and EPOC effect at 350°C, by finely dispersing the Fe nanowires on Co3O4 to expose active sites and lowering the rate of sintering while being conductive to close the circuit[5]. As opposed to using other supports that do not display fully conductive properties, this approach provides an electronic path for the promoters to follow. Results have shown the working-catalyst FeOx/Co3O4 on YSZ and BZY to be highly selective to CO formation under oxidizing (3CO2:H2) and reducing (CO2:7H2) conditions, with a superior activity experienced under rich reducing conditions. Furthermore, alteration in work function from the EPOC effect, has led to a promotional response for both YSZ and BZY. Combining the MSI and EPOC effect allows for high RWGS activity, establishing a promising solution in utilizing CO2 as a resource while using transition metals. Additionally, the EPOC effect will be elucidated through Fourier-Transform Infrared (FTIR) spectroscopy to provide insight on the promoting mechanism occurring during polarization. 1. Porosoff, M. D., Yan, B. & Chen, J. G. Catalytic reduction of CO2 by H2 for synthesis of CO, methanol and hydrocarbons: challenges and opportunities. Energy Environ. Sci. 2, 303 (2015).1. Baranova, E. A., Bock, C., Ilin, D., Wang, D. & MacDougall, B. Infrared spectroscopy on size-controlled synthesized Pt-based nano-catalysts. Surf. Sci. 600, 3502–3511 (2006).2. Panaritis, C., Edake, M., Couillard, M., Einakchi, R. & Baranova, E. A. Insight towards the role of ceria-based supports for reverse water gas shift reaction over RuFe nanoparticles. J. CO2 Util. 26, 350–358 (2018).3. Vayenas, C. G., Bebelis, S., Pliangos, C., Brosda, S. & Tsiplakides, D. Electrochemical Activation of Catalysis. (Springer US, 2001).4. Zagoraios, D. et al. Electrochemical promotion of methane oxidation over nanodispersed Pd/Co3O4 catalysts. Catal. Today (2019). doi:10.1016/j.cattod.2019.02.030

Thermal energy capture by pyroelectric effect

Taking advantage of the physical nature of the pyroelectric materials, in this investigation a characteristic of these materials known as the pyroelectric effect was studied and corroborated, which allows this type of materials are sensitive to infrared electromagnetic radiation, and whose response can be seen in the form of electric potential difference. In this way, in this document the theoretical basis of operation of this effect is presented, and in turn, the results of experiments carried out in laboratories of the University of Santo Tomás Bogotá D.C. The experiments were performed using the “PIR325” sensor, which is composed of two thin films of pyroelectric material. In the first instance, the response of the sensor to thermal electromagnetic radiation produced by the human body is obtained, in the second instance, the same experiment is repeated, However, on this occasion, a Fresnel lens is used to ensure the highest infrared electromagnetic energy collection. Finally, the capture of the signals obtained in each experiment is performed and the results are contrasted, where the theoretical basis of the pyroelectric effect is demonstrated, and in turn, the importance of using a Fresnel lens in applications to carry out this type of sensors.

Chloride involvement in the synthesis, functioning and repair of the photosynthetic apparatus in vivo.

Cl- has long been known as a micronutrient for oxygenic photosynthetic resulting from its role an essential cofactor for photosystem II (PSII). Evidence on the in vivo Cl- distribution in Spinacia oleracea leaves and chloroplasts shows that sufficient Cl- is present for the involvement in PSII function, as indicated by in vitro studies on, among other organisms, S.oleracea PsII. There is also sufficient Cl- to function, with K+ , in parsing the H+ electrochemical potential difference (proton motive force) across the illuminated thylakoid membrane into electrical potential difference and pH difference components. However, recent in vitro work on PSII from S.oleracea shows that oxygen evolving complex (OEC) synthesis, and resynthesis after photodamage, requires significantly higher Cl- concentrations than would satisfy the function of assembled PSII O2 evolution of the synthesised PSII with the OEC. The low Cl- affinity of OEC (re-)assembly could be a component limiting the rate of OEC (re-)assembly.

Dynamic electron transfer for reducing nanofriction of graphene at electrified interfaces

Nanofriction properties of graphene at electrified interfaces are important for the application of graphene as a solid lubricant in graphene-based electric-carrying interfaces. The nanofriction experiments based on conductive atomic force microscopy show that dynamic electron transfer determines nanofriction of graphene at the electrified interfaces. Nanofriction at highly conductive interfaces remain constant because the fast electron transfer decreases the electrical potential difference. However, nanofriction at low conductive interfaces increases because electron blocking increases the electrical potential difference. The nanofriction of graphene correlated negatively with loads at low conductive interfaces because high loads decrease the contact resistance to release blocked electrons. Furthermore, large graphene possesses higher nanofriction than small graphene. Scanning Kelvin force microscopy measurements show that the larger electron capacity of large graphene can maintain the electrical potential difference at interfaces. These studies provide beneficial guidelines for the applications of graphene as a solid lubricant at electrified interfaces.

Electric current generation of a droplet falling into an electrolyte solution

A novel system which can greatly improve the waving potential [1] of metal produced by a moving liquid–solid boundary is presented in this paper. By using a pair of copper electrodes immersed in an electrolyte solution, a significant electric potential is generated by changing the wetted surface area of only one electrode when a droplet falls into the electrolyte solution. Experiments show that the electric potential difference between the two electrodes is generated due to different wetted areas at the two electrodes. The magnitude of the generated electric current depends on the types of the electrolyte solution and the moving speed of the air-electrolyte solution interface. A droplet of 24 µL can generate a waving potential of three orders of high than that reported in the reference paper [1]. The approach of inserting a pair of asymmetrically insulated metal electrodes into an electrolyte solution makes it possible to utilize ordinary pure metal materials for harvesting waving potential energy from a dynamic moving liquid–air interface.

Pressure-driven ion separation through a pH-regulated cylindrical nanopore

The ion rejection performance of a pH-regulated cylindrical nanopore is studied comprehensively. We show that this performance can be assessed by the ion selectivity of the nanopore. A larger ion selectivity yields a greater electric potential difference across the nanopore to balance ion transport, thereby lowering the rate of salt transport. Although the electrostatic interaction between mobile ions and the nanopore surface leads to salt rejection, increasing the surface charge density and/or the nanopore length raises the rejection only up to a certain extent. Due to the decrease in the ion selectivity and the increase in the strength of the induced electric field having a direction opposite to that of the liquid flow, the shorter the nanopore the smaller the rejection. In this case, the volumetric flow rate deviates more significantly from Hagen-Poiseuille equation than pores with length ranging from 100 nm to few micrometers. The radius of a nanopore is more significant than its length in influencing the rejection. Depending upon the value of nanopore radius, the rejection shows either an asymptotic value or a local maximum as the applied transmembrane pressure increases. The rejection can be improved remarkably by lowering the nanopore radius because the electrostatic interaction between mobile ions and the nanopore surface increases significantly. Nonintuitively, larger pores show better rejection performance in low-pressure filtration than smaller pores. The asymmetric fixed charge distribution on the nanopore surface arising from its pH-regulated nature is capable of tuning the net ion concentration gradient inside it.